1. Technical Field
The present invention pertains to regulator devices. In particular, the present invention pertains to regulator devices for delivering low concentrations of corrosive and reactive gas mixtures.
2. Discussion of the Related Art
Regulators are utilized in fluid flow systems to reduce the pressure of a fluid to a lower, safer level that facilitates use of the fluid within the systems. In particular, two-stage regulators are very effective in maintaining the flow of fluid from the outlet of the regulator at a substantially constant pressure despite variations in inlet pressure.
An important function of a regulator is to provide pressure regulation without altering the composition of the fluid by a reaction of one or more fluid components with the internal surface of the regulator. This is a very important issue when dealing with reactive or corrosive gases, such as hydrogen sulfide, sulfur dioxide, carbonyl sulfide, mercaptans, hydrogen chloride, chlorine, ammonia, nitric oxide, nitrous oxide, nitrogen dioxide, carbon monoxide, carbon dioxide, arsine, volatile organic carbons or VOC's, and oxygenates.
For example, hydrogen sulfide (H2S) is known to react with copper to form copper sulfide and hydrogen. Use of a regulator having copper components with a hydrogen sulfide gas would result in a small amount (e.g., a few hundred parts-per-million or ppm) of the hydrogen sulfide gas reacting with, and adsorbing onto, the internal copper surfaces of the regulator. While such small amounts of the gas being consumed may not be noticed, particularly when processing a high concentration hydrogen sulfide gas, prolonged use of the regulator with this gas would result in its degradation and eventual failure. Further, if a regulator made with copper components and/or other materials that are reactive with the gas were to be used for relatively low concentrations of hydrogen sulfide, much or all of the hydrogen sulfide would react with and/or adsorb onto the internal regulator surfaces. Therefore, regulators constructed of copper and/or other reactive materials are not desirable for use with reactive gases at low concentrations.
The reaction of hydrogen sulfide or other reactive gases with the regulator internal surfaces may be limited or substantially avoided by using non-reactive or less reactive materials to form the regulator. In particular, stainless steel (e.g., 316 stainless steel) is commonly used in regulators designed for providing corrosive gas service. Alternatively, brass regulators may be coated with chrome or nickel to improve corrosion resistance. However, it is often difficult to provide a conformal coating to the entire internal brass surfaces of the regulator with chrome or nickel, so a small amount of brass surfaces tend to remain exposed for reaction with gases flowing within the regulator.
Although the use of non-reactive or less reactive materials can limit or prevent the reaction of the gas with the internal surfaces of the regulator, the gas may still adsorb to the internal surfaces of the regulator during operation, resulting in a reduced concentration of reactive gas exiting the regulator at least during an initial use period for the regulator. Many conventional regulators employ a circuitous flow path through the regulator that may include as many as four or more 90° bends between the regulator inlet and outlet. The circuitous flow path results in a large internal surface area and volume of the regulator, which in turn increases the time for which gases may react with wet surfaces and/or adsorb to internal surfaces of the regulator.
Another important consideration that is associated with large internal surface areas is how much of the internal surfaces of the regulator may be wetted. The reactive gases can react with wetted internal surfaces of the regulator, resulting in corrosion of the regulator.
Due to the nature of reactive gases and the probability of reactivity and/or adsorption that can occur between the reactive gases and the internal surfaces of a regulator, conventional regulators typically must be passivated for a sufficient period of time before being placed in service. For example, a period of several hours or even days may be required to passivate a conventional stainless steel regulator in order to ensure that adsorption and/or reactions of reactive gases on the internal surfaces of the regulator are substantially complete so that the regulator can deliver reactive gases at a desired concentration level.
For fluid flow systems that require the measurement of low levels of reactive compounds within the gas flowing in the system, the previously noted issues become a significant concern and reliable equipment and techniques are necessary to monitor, control and regulate the gaseous compounds being delivered in such systems. Instrument manufacturers have been decreasing the lower level of detection of gaseous compounds into the low parts-per-billion (ppb) range. For example, sulfur-containing standards are now available at concentrations of 50–100 ppb. While conventional stainless steel regulators may be employed to process low concentration reactive gases, these regulators must first be passivated before being implemented for use, which can require a considerable amount of time. In addition, these large surface area regulators are more susceptible to having wet areas and are not as easy to thoroughly dry prior to use.
Thus, there exists a need for a regulator adapted to reliably deliver low concentration reactive gas mixtures for processing in a flow system that requires little or no passivation prior to being implemented for use in a fluid flow system.